(1) Field of the Invention
The present invention relates to an undercarriage, to an aircraft having at least one retractable undercarriage, in particular a rotorcraft of the helicopter type, and to a method of landing said aircraft.
(2) Description of Related Art
Conventionally, an aircraft includes landing gear having a plurality of undercarriages.
In order at least to minimize aerodynamic drag of an undercarriage during cruising flight, so as to obtain an aircraft capable of flying at high speed or over a long distance, it is known to retract the undercarriages into suitable housings.
Two alternative installations can then be distinguished.
In a first type of installation, a streamlined fairing is used, sometimes known as a “sponson” by the person skilled in the art, with the undercarriage then being retracted in flight into the housing as defined in particular by the streamlined fairing.
Although advantageous, that first type of installation presents the drawback of requiring projecting fairings that generate non-negligible aerodynamic drag. The saving in drag that is achieved by retracting the undercarriage in cruising flight is thus diminished by the aerodynamic drag due to the fairings covering the landing gear.
In a second type of installation, the landing gear is arranged in a landing-gear well, i.e. a housing that is arranged in the airframe of the aircraft. The well may be closed by a movable hatch suitable for reconstituting the skin of the aircraft locally.
That second type of installation thus does not generate any additional aerodynamic drag in flight. Nevertheless it presents the drawback of requiring large housings that are found to be penalizing in terms of weight. Furthermore, it is sometimes difficult to obtain the necessary volume inside the airframe.
In addition, a portion of the undercarriage is sometimes located between load-carrying frames for a cabin of the aircraft, and this location can constitute a source of noise and indeed can lead to elements of the undercarriage intruding into the cabin in the event of an accident.
An undercarriage is sometimes designed not only to absorb the energy that results from a normal landing, but also to absorb the energy that results from an emergency landing, in other words during a crash of the aircraft under emergency conditions as specified in certification regulations, for example.
The undercarriage then includes an undercarriage leg supporting contact means, e.g. a wheel, and it may also include an actuator-shock absorber. The actuator-shock absorber serves firstly to tilt the undercarriage leg in order to deploy it or retract it as required, and secondly to absorb at least some of the energy that results from an emergency landing.
Such an actuator-shock absorber may include a low-pressure space that is used to perform the deployment/retraction function of the undercarriage leg, and a high-pressure space that is used to perform the shock absorber function that is to dissipate the energy of an emergency landing.
Arranging an anticrash undercarriage in a small space without giving rise to high levels of aerodynamic drag thus turns out to be complex.
Furthermore, it should be observed that during a crash, the undercarriage retracts into its housing. When the housing is an undercarriage well formed in the aircraft airframe, the undercarriage runs the risk of passing through the walls defining the housing and possibly penetrating into the aircraft cabin, for example.
Document EP 0 275 735 describes an actuator-shock absorber, and also an undercarriage fitted with such an actuator-shock absorber.
Contact means are arranged at the end of an undercarriage leg that is suitable for pivoting about a pivot axis parallel to the transverse axis of the aircraft and thus perpendicular to the anteroposterior plane of symmetry of said aircraft.
Furthermore, an actuator-shock absorber is hinged to said undercarriage leg, the actuator-shock absorber being substantially parallel to the elevation axis of the aircraft.
The function of the actuator-shock absorber is to retract the contact means into a streamlined fairing, and to enable energy to be absorbed during landing. That actuator-shock absorber thus runs the risk of penetrating in unwanted manner into the airframe in the event of an emergency landing.
Document FR 2 689 087 presents an undercarriage having an undercarriage leg, the undercarriage leg comprising a first element and a second element that are hinged to each other about a pivot axis.
A shock absorber is also arranged between the first and second elements.
In addition, the first element is provided with contact means while the second element is provided with an actuator-shock absorber suitable for causing the contact means to retract by pivoting about the pivot axis.
It should be observed that during a crash, the contact means return into the housing, with this movement of the contact means being identical both during a crash and during retraction.
Document FR 2 383 070 describes an undercarriage having an undercarriage leg carrying contact means via an axle and a bent lever, the undercarriage leg being hinged to an aircraft via a universal joint.
In addition, the undercarriage includes a shock absorber hinged via a first universal joint to the undercarriage leg and to the aircraft via a second universal joint.
Finally, the undercarriage includes a driving and bracing actuator as opposed to an actuator-shock absorber, which actuator is hinged to the aircraft via a first universal joint and to the undercarriage leg via a second universal joint.
In the event of a crash, and like document FR 2 689 087, the contact means return into the housing, with the movement of the contact means being identical both during a crash and during retraction.
Documents EP 1 721 827 and EP 1 714 870 are also known.